Apparatus for testing the road-tire adhesion of a vehicle

ABSTRACT

The apparatus gives information relative to the road-tyre adhesion of a vehicle, comprising an electronic anti-skid device so as to allow the driver to appraise or to know the distance over which move during a panic braking before coming to a stop or before slowing down to a safe speed. The apparatus comprises a pulse-width measuring circuit for measuring the duration of the isolation signals which are developed in the anti-skid device for temporarily isolating the braking system. The information can be displayed by colored lamps. However, the apparatus can comprise more elaborate indicating means delivering signals which can be converted into direct readings or into signals representative of the theoretical braking distance. The comparison of these signals with signals delivered by a range finding device measuring the distance separating the vehicle from an obstacle ahead allows a warning signal to be obtained when the distance is unsafe.

United States Patent 1 1 Furia 1 1 Nov. 13, 1973 [75] Inventor:AndrFuria,Neuilly,France [73] Assignee: Societe Anonyme D.B.A., Paris,

France [22] Filed: May 17, 1971 [21] Appl. No.: 144,146

[30] Foreign Application Priority Data May 20, 1970 France 7018318 [52]US. Cl. 343/13 R, 73/146, 303/21 R [51] Int. Cl G018 9/06, B60t 8/06[58] Field of Search 303/21 AF, 21 P;

73/146, 9; 343/7 ED, 13 R; 235/151.32, 150.24; 180/82 OTHER PUBLICATIONSSkolnik, M. 1., Introduction to Radar Systems, McGraw-Hill, 1962, pp.555, 556.

Millman & Taub, "Pulse, Digital, and Switching Waveforms," McGraw-Hill,1965, pp. 2735, pp. 38 -40.

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-G. E. MontoneAttorneyW. N. Antonis and Plante, Hartz, Smith and Thompson [57]ABSTRACT The apparatus gives information relative to the roadtyreadhesion of a vehicle, comprising an electronic anti-skid device so asto allow the driver to appraise or to know the distance over which moveduring a panic braking before coming to a stop or before slowing down toa safe speed. The apparatus comprises a pulse-width measuring circuitfor measuring the duration of the isolation signals which are developedin the anti-skid device for temporarily isolating the braking system.The information can be displayed by colored lamps. However, theapparatus can comprise more elaborate indicating means deliveringsignals which can be converted into direct readings or into signalsrepresentative of the theoretical braking distance. The comparison ofthese signals with signals delivered by a range finding device measuringthe distance separating the vehicle from an obstacle ahead allows awarning signal to be obtained when the distance is unsafe.

6 Claims, 2 Drawing Figures PATENTEUHHY 13 I913 SHEET 1 OF 2PMENTEDHHVUIBYS 1177 SHEET 2 UF 2 y SP5 GHVERAm/P //v0/'6 r0/? RADAR/ wCOMPUTER INDICATOR COMPARISON 5 CIRCUIT I 1 WA HIV/N6 DEV/CE APPARATUSFOR TESTING THE ROAD-TIRE ADHESION OF A VEHICLE This invention relatesto an apparatus for testing the road-tire adhesion or gripping abilityof a vehicle having a braking system equipped with an electronicantiskid device.

An anti-skid device substantially reduces the braking distances andimproves the directional stability during braking. However, it may befeared that some drivers will gain an excessive confidence from thefeeling of safety given by the anti-skid device, so as to wrongfullybelieve that they are able to stop very quickly at any moment, whereasin fact the braking distance varies as a function of the adhesionbetween the road and the tires of the vehicle.

It is known that, in the course of a braking operation, an anti-skiddevice develops isolation signals for creating recurrent periods duringwhich the braking system is isolated. it has been remarked that theisolation signals have a duration which is a function of the road-tireadhesion.

Taking advantage of this remark, it is an object of the invention toprovide an apparatus for supplying a driver with information relative tothe road-tire adhesion, allowing him to estimate or to know the distanceover which his vehicle will move during a panic braking before coming toa complete stop or before reaching a reduced speed compatible withsecurity.

According to the invention, the isolation signals are applied to theinput of a pulse-width measuring circuit, the output of this circuitbeing connected to indicating means. In a preferred embodiment, thepulse-width measuring circuit comprises a derivating circuit producing afirst pulse in response to the leading edge of each isolation signal anda second pulse in response to the trailing edge of the signal, amonostable circuit triggered by the first pulse, and at least onetwo-input AND gate, the second pulse being applied to one input of thegate, while the output of the monostable circuit is connected to theother input of the gate, and the output of the gate constitutes theoutput of the pulse-width measuring circuit.

When the indicating means comprises a few visible or audible indicators,for example green, yellow, and red lamps indicating a good, medium orbad road-tire adhesion, the succint information displayed is sufficientfor rousing the driver's attention.

It will be noted that the information depends not only upon the roadcondition, but also upon the degree of wear of the tires. For example,if the red lamp is displayed when the road is hardly wet, the driverwill know that the tires need replacing.

However, with more elaborate indicating means, a substantially accuratevalue of the coefficient of adhesion can be obtained. This information,combined with an information relative to the vehicle speed, can besupplied to a computer circuit conceived for issuing an informationrelative to the braking distance.

The invention will now be described by way of example with reference tothe accompanying drawings in which FIG. 1 is the diagram of an apparatusaccording to the invention FIG. 2 is the block-diagram of a warningsystem incorporating the apparatus according to the invention.

Referring to FIG. 1, the apparatus for testing the gripping aptitude ofa vehicle comprises a multi-stage monostable circuit having three stagesM1, M2, M3, an amplifier A and three AND gates P1, P2, P3. Each of theAND gates receives a signal from the amplifier and from one of themonostable stages, and delivers a signal to an indicating device V, J orR through a timing device N1, N2, or N3.

The monostable circuit is of a conventional type. Each stage of thecircuit comprises a NPN transistor having an emitter electrode connectedto ground, the base and collector electrodes being connected to thepositive terminal of a voltage source through respective resistors. Acondenser is connected between the collector of the transistor in one ofthe stages and the base of the transistor in the next stage. When apulse is applied on the condenser connected to the base of thetransistor in the first stage M1, the collector of this transistordelivers an output signal having a duration which is a function of thedischarging time of the condenser. The end of this signal initiates asignal in the next stage, and so on. The signals in the various stagesmay have equal or different durations.

Each of the AND gates Pl,P2,P3, may be constituted by a transistorhaving a base electrode connected to the output of the amplifier Athrough respective resistors R1,R2,R3, and a collector electrodeconnected to the output of one stage in the monostable circuit. Theemitter electrodes of these transistors are connected to the inputterminals of the timing devices N1, N2, N3, respectively.

The amplifier A is constituted by a transistor of the NPNtype having anemitter electrode connected to ground, and having base and collectorelectrodes connected to the positive terminal of the voltage sourcethrough resistors R4, R5, respectively.

The timing devices N1,N2,N3, may be constituted by conventional triggercircuit and, for simplification purposes, they are shown as plainsquares. These timing devices serve to extend the duration of the outputsignals delivered by the AND gates. They are necessary only when theindicating devices have a relatively slow response, or when the signalsfeeding the indicating devices must have a longer duration than theoutput sig nals of the AND gates, which occurs for example when lampsare used as indicating devices.

The apparatus further comprises a differentiating circuit in which acondenser Cd and a series resistor Rd are connected between an inputterminal E and ground. The common point of the condenser Cd and theresistor Rd is simultaneously connected to the oathode electrode of adiode D1 and to the anode electrode of a diode D2, the cathode of diodeD2 being connected to the control electrode of amplifier A, while theanode of diode D1 is connected to the input of a pulse-shaping stagecomprising a transistor T and resistors R6, R7, the collector oftransistor T being connected to the condenser in the first stage Ml ofthe monostable circuit. The direction in which the diodes D1 and D2 areconnected is such that diode D1 is conducting when the derivatingcircuit issues a positive signal and the diode D2 is conducting when thederivating circuit issues a negative signal.

The input terminal E is adapted to receive isolation signals which aredeveloped a number of times during a brake application for momentarilyisolating the braking system of a vehicle equipped with an anti-skiddevice.

In the operation, responsive to the leading edge of the isolationsignal, the differentiating circuit Cd-Rd issues a positive pulse which,through the diode D1 and through the pulse-shaping transistor T,triggers the first stage M1 in the monostable circuit. Responsive to thetrailing edge of the isolation signal, the derivating circuit Rd-Cdissues a negative pulse which is applied to the input of the amplifier Athrough the diode D2 and gives rise to an amplified output signal whichis transmitted to the base electrodes of the transistors P1,P2,P3.

If the trailing edge of the isolation signal appears while the firststage Ml of the monostable circuit is delivering an output signal, thetransistor Pl will shift to the conducting state, thus delivering anactuating signal to the timing N1, hence to the indicating device V. Inthis case, the isolation signal has a short duration, and it indicatesthat the vehicle adhesion is good.

However, if the isolation signal extends intime beyond the relaxationtime of the first stage M1, the output signal of the stage M] willvanish and be replaced by the output signal of the stage M2 and possiblythis latter signal will be replaced by the output signal of the stageM3. If the isolation signal ends prior to the relaxation of the stageM2, the transistor P2 will shift to the conducting state, thusenergizing the indicating device I to indicate a medium adhesion of thevehicle. If the isolation signal ends after the relaxation of the stageM2, the transistor P3 will become conducting to energize the indicatingdevice R and display the information that the vehicle adhesion is bad.

When the indicating devices are few in number, for example three innumber as in FIG. 1, they may be constituted by colored lamps. One orthe other of the lamps is switched on every time the driver depressesthe brake pedal. At any moment, the driver may apply the brakes brieflyfor testing the vehicle adhesion.

However, the number of indicating devices may be as great as desired, itbeing sufficient that the AND gates and the monostable stages areprovided in equal number. The indicating devices can be so devised as todeliver coded signals or stepped voltages from which fairly accuratevalues of the vehicle gripping factor can be obtained either in the formof electrical signals or in the form of direct readings.

FIG. 2 is the block-diagram of a system in which the apparatus of theinvention, 1, giving values of the gripping factor p. of a vehicle, isused for finding the theoretical braking distance F1, and for comparingthis distance F1 to the actual distance F2 separating the vehicle froman obstacle such as a vehicle ahead.

The braking distance is obtained from the equation Fl V'l2 ig in which Vis the vehicle speed and g the acceleration of gravity.

In the system illustrated in FIG. 2, the output signals of the apparatus1 and the output signals of a speed indicator 2 are processed in acomputer 3 which feeds an indicator 4 with signals proportional to W121, g, hence proportional to the theoretical distance Fl. A comparisoncircuit simultaneously receives these signals and signals delivered byan acoustical or electromagnetical range finding apparatus such as aradar 6, used for measuring the actual distance F2. The output terminalof the comparison circuit is connected to a warning device 7. Thewarning device is energized by the output signals of the comparisoncircuit when the theoretical braking distance F1 is greater than theactual distance F2.

A brief application of the brakes allows the driver to read thetheoretical braking distance F l on the indicator 4. Moreover, thewarning device 7 issues a visible or audible signal when the vehicleahead is insufficiently distant for avoiding a collision if this vehiclestops abruptly.

1n the system just described, it is assumed that the vehicle ahead canstop instantaneously. In fact, this vehicle will move over a certaindistance before coming to a complete stop. This might be taken intoaccount, but caution recommends not to do so, because account must alsobe taken of the time which elapses from the moment when the driver aheadinitiates a braking operation to the moment when the following driver isaware of this fact.

What is claimed is: 1. In a wheeled vehicle having an antiskid systemresponsive to the rotational speed of a vehicle wheel for generating anisolating signal controlling the brake associated with said wheel,apparatus for testing the roadtire adhesion of the vehicle comprising:

means for differentiating said isolating signal to produce a first pulsein response to the leading edge of said isolating signal and a secondpulse in response to the trailing edge of said isolating signal;

monostable circuit means triggered by said first pulse to produce anoutput signal; gating means producing an output signal when both saidsecond pulse and the output signal from said monostable circuit meansare transmitted to said gating means, whereby the output signal of saidgating means indicates that the time lapse between the first and secondpulses is less than the relaxation time of the monostable circuit means;and

indicating means responsive to the output signal of said gating means.

2. The invention of claim 1:

there being a plurality of said gating means and a correspondingmonostable circuit means connected in cascade for each of said gatingmeans, the output of each of said monostable gating means beingconnected to an input of a corresponding gating means, and meanstransmitting said second pulse to another input of each of said gatingmeans simultaneously.

3. The invention of claim 1; and

a timing device connected between the indicating means and the output ofsaid gating means.

4. The invention of claim 3:

said indicating means including at least one lamp.

5. The invention of claim 1:

means for generating a speed signal proportional to the velocity of saidvehicle wheel; and

means responsive to said speed signal and to the output signal of saidgating means for generating a signal proportional to the theoreticaldistance required to stop the vehicle.

6. The invention of claim 5:

range finding means for generating a signal proportional to the distancebetween said vehicle and an obstacle ahead of said vehicle; and

6 comparator means for comparing said signal proporever the theoreticaldistance to stop the vehicle is "Dual to the d'smnce between the veh'cleand an greater than the distance between the vehicle and obstacle aheadof said vehicle with said signal representing the theoretical distancerequired to stop the vehicle and actuating a warning device when- 5 anobstacle ahead of said vehicle.

l i l I!

1. In a wheeled vehicle having an antiskid system responsive to therotational speed of a vehicle wheel for generating an isolating signalcontrolling the brake associated with said wheel, apparatus for testingthe road-tire adhesion of the vehicle comprising: means fordifferentiating said isolating signal to produce a first pulse inresponse to the leading edge of said isolating signal and a second pulsein response to the trailing edge of said isolating signal; monostablecircuit means triggered by said first pulse to produce an output signal;gating means producing an output signal when both said second pulse andthe output signal from said monostable circuit means are transmitted tosaid gating means, whereby the output signal of said gating meansindicates that the time lapse between the first and second pulses isless than the relaxation time of the monostable circuit means; andindicating means responsive to the output signal of said gating means.2. The invention of claim 1: there being a plurality of said gatingmeans and a corresponding monostable circuit means connected in cascadefor each of said gating means, the output of each of said monostablegating means being connected to an input of a corresponding gatingmeans, and means transmitting said second pulse to another input of eachof said gating means simultaneously.
 3. The invention of claim 1; and atiming device connected between the indicating means and the output ofsaid gating means.
 4. The invention of claim 3: said indicating meansincluding at least one lamp.
 5. The invention of claim 1: means forgenerating a speed signal proportional to the velocity of said vehiclewheel; and means responsive to said speed signal and to the outputsignal of said gating means for generating a signal proportional to thetheoretical distance required to stop the vehicle.
 6. The invention ofclaim 5: range finding means for generating a signal proportional to thedistance between said vehicle and an obstacle ahead of said vehicle; andcomparator means for comparing said signal proportional to the distancebetween the vehicle and an obstacle ahead of said vehicle with saidsignal representing the theoretical distance required to stop thevehicle and actuating a warning device whenever the theoretical distanceto stop the vehicle is greater than the distance between the vehicle andan obstacle ahead of said vehicle.